The aim of the proposed study is to determine physiological and immunological conditions necessary to extend survival of small bowel allografts as functioning organs. Transplantation of the entire small bowel will be performed in inbred rat strains with a spectrum of immunogenetic disparity. This will be a baseline study to obtain median survival times of varying length. Graft position in relation to the recipient's own gastrointestinal tract (orthotopic as functional loop versus heterotopic as Thiery Vella loop) and site of venous outflow (into inferior vena cava or portal vein) will be evaluated as to their effects upon survival and function of small bowel allografts. (1) Non-specific immunotherapy (ALS, splenectomy), (2) elimination of passenger leukocytes within the graft (by ALS, X-irradiation) and (3) two enhancement protocols will be studied as approaches to extend survival of small intestinal allografts. Small bowel which is replete with lymphoid tissues, has the potential to induce a lethal graft versus host (GvH) reaction. The efficacy of ALS and X-irradiation for control of the GvH-reaction will be investigated. Intestinal glucose, maltose and lactose absorption will be evaluated as test of graft performance and as test with predictive value for imminent graft rejection.